2011 is the best format by far. Big basics like darkrai ex , mewtwo ex, terrakion, and tornadus centralize the meta. Decks like CMT, junk hunt darkrai, darkrai terrakion, and mixes of them force out cards like machamp and donphan prime that turn into worse versions of a retaiate from terrakion.
2012 was the start of mewtwo wars, and heavy switch/sky arrow bridge lines to move around the same 5 pokemon to avoid resistances. If your opponent has darkrai active, switch terrakion. Terrakion active? switch mewtwo. DCEs and dead draws decide games rather than deck building and well thought out play.
2011 on the other hand has at least 5 good cards of any type you could imagine. Although 2011 giants could still compete in 2012, stage two decks became harder and harder to pull off when reshiram and zekrom can do 120 as a basic. Magnezone prime allows you to run through your deck for resources, yanmega prime rewards thought out play with copycats, judges, pont, and search/discard cards. I could write pages about why 2011 is one of, if not the best format.
Almost every card printed in the triumphant set has a niche and can be used well. Triumphant Best Set